1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a liquid crystal display capable of realizing a reflection mode through a transmissive liquid crystal display and a method of driving the same.
2. Discussion of Related Art
In a conventional liquid crystal display (LCD), two substrates are arranged so that respective surfaces, on which electric field generating electrodes are positioned to face each other. Liquid crystal is inserted between the two substrates, and a voltage is applied to the two electrodes to generate an electric field by which liquid crystal molecules are moved so that an image is displayed by the transmittance of light that varies with the movement of the liquid crystal molecules.
An active matrix liquid crystal display (AM-LCD) includes pixels that have thin film transistors (TFTs) that are switching devices that open and close the pixels. The AM-LCD type of liquid crystal display is the most spotlighted type, since the AM-LCD has high resolution and moving picture realizing ability.
Hereinafter, the lamination structure of a common LCD will be described with reference to FIG. 1.
FIG. 1 is a schematic perspective view of a common LCD. First and second substrates 10 and 30 are arranged to face each other, a plurality of gate wiring lines 12 and data wiring lines 14 that cross each other are on the internal surface of the first substrate 10, TFTs T are in the crossed regions between the gate wiring lines 12 and the data wiring lines 14, and pixel electrodes 16 connected to the TFTs T are in pixel regions P defined by the crossed regions between the gate wiring lines 12 and the data wiring lines 14.
Storage capacitors Cst (not shown) for storing data signals applied through the data wiring lines 14 for one frame period are included in respective pixel regions. The storage capacitors are composed of first electrodes (not shown) arranged to run parallel to the gate wiring lines 12 and second electrodes (not shown) on the first electrodes with an insulating layer interposed between them.
Color filter layer 32 and common electrodes 34 are sequentially positioned on the internal surface of the second substrate 30 and a liquid crystal layer 50 is interposed between the pixel electrodes 16 and the common electrodes 34.
Black matrices (BMs) are between the color filter layers 32 in the regions of the TFTs T and the storage capacitors Cst on the first substrate to prevent light from leaking.
First and second polarizers 52 and 54 are arranged on the rear surfaces of the first and second substrates 10 and 30 and a backlight that is a light source device for supplying light is arranged on the rear surface of the first polarizer 52.
According to the conventional LCD, light generated by the backlight passes through the respective cells, that is, the pixel regions of the LCD so that only 7% of the light is actually transmitted on a screen. Therefore, the backlight is made brighter in order to provide an LCD with high brightness. Increasing the brightness of the backlight, however, increases power consumption.
Therefore, a heavy battery is used as a power source of the backlight. However, the battery has limitations on use time.
In order to solve the problem, a semi-transmissive LCD that has both a transmissive mode in which light of the backlight is used and a reflection mode in which external light is used has been studied and developed.
The reflective-transmissive LCD has both the function of a transmissive LCD and the function of a reflective LCD so that the reflective-transmissive LCD can use light of the backlight and an external natural or artificial light source. Therefore, it is possible to reduce power consumption without being restricted by peripheral circumstances.
However, according to the conventional reflective-transmissive LCD, reflecting electrodes that form reflecting units in partial regions of the pixel regions on the first substrate are added and a retardation film (quarter wave plate (λ/4)) is added between a polarizer and a panel.